This invention relates to heat shielded enclosures for protecting and preserving a device or assembly from an otherwise destructive high temperature environment and, particularly, to heat shielded enclosures wherein enclosure size and weight is an important consideration. In the disclosed embodiment, this invention specifically relates to a compact, lightweight memory unit for use in a crash survivable aircraft flight data recorder wherein the memory unit is configured to withstand an aircraft crash and an ensuing fire with little or no loss of stored data.
Although there are numerous situations in which it is necessary or desirable to protect an item, device or assembly from deleterious exposure to a high temperature environment, shielding the memory device of an aircraft flight recorder system during crash and a fire presents extremely demanding design constraints. In this regard, in order to preserve flight data supplied to the memory unit by the flight data recorder data acquisition unit during a predetermined time interval immediately prior to an aircraft crash, the memory unit must be configured and arranged to withstand temperatures in excess of 1100.degree. C. (approximately 2000.degree. F.), experienced during a fire while simultaneously being constructed to endure crushing and penetration forces experienced either on impact or during secondary impact with other portions or pieces of the aircraft. Further, the memory unit of a flight data recorder system is subject to additional design constraints imposed by considerations generally applicable to aircraft equipment and systems, including constraints relating to size, weight, cost, serviceability and reliability.
Technical advances in the various electronic solid state device arts have led to high capacity electronic memory devices for nonvolatile storage of digitally encoded data with programmable read only field effect transistor devices and bubble memory devices being two types of such memories. Because such devices are small and lightweight and exhibit high reliability, there has been substantial impetus for replacing the magnetic tape transports utilized in current flight recorder system designs with solid state memories.
Because of increased heat shielding demands, the currently employed technique of mounting a tape transport or other flight data recorder memory device within a cavity that is formed by encasing the memory device with a solid material that is a relatively good thermal insulator and surrounding that assemblage with a protective metal housing does not achieve the desired overall reduction in memory unit size and weight that might be obtained in flight data recorder systems employing semiconductor memory devices such as erasable programmable read only memories.